666 research outputs found
Advanced System Design Requirements for Large and Small Fixed-wing Aerial Application Systems for Agriculture
Several candidate aircraft configurations were defined over the range of 1000 to 10,000 pounds payload and evaluated over a broad spectrum of agricultural missions. From these studies, baseline design points were selected at 3200 pounds payload for the small aircraft and 7500 pounds for the large aircraft. The small baseline aircraft utilizes a single turboprop powerplant while the large aircraft utilizes two turboprop powerplants. These configurations were optimized for wing loading, aspect ratio, and power loading to provide the best mission economics in representative missions. Wing loading of 20 lb/sq ft was selected for the small aircraft and 25 lb/sq ft for the large aircraft. Aspect ratio of 8 was selected for both aircraft. It was found that a 10% reduction in engine power from the original configurations provided improved mission economics for both aircraft by reducing the cost of the turboprop. Refined configurations incorporate a 675 HP engine in the small aircraft and two 688 HP engines in the large aircraft
VLBI astrometry of PSR J2222-0137: a pulsar distance measured to 0.4% accuracy
The binary pulsar J2222-0137 is an enigmatic system containing a partially
recycled millisecond pulsar and a companion of unknown nature. Whilst the low
eccentricity of the system favors a white dwarf companion, an unusual double
neutron star system is also a possibility, and optical observations will be
able to distinguish between these possibilities. In order to allow the absolute
luminosity (or upper limit) of the companion object to be properly calibrated,
we undertook astrometric observations with the Very Long Baseline Array to
constrain the system distance via a measurement of annual geometric parallax.
With these observations, we measure the parallax of the J2222-0137 system to be
3.742 +0.013 -0.016 milliarcseconds, yielding a distance of 267.3 +1.2 -0.9 pc,
and measure the transverse velocity to be 57.1 +0.3 -0.2 km/s. Fixing these
parameters in the pulsar timing model made it possible to obtain a measurement
of Shapiro delay and hence the system inclination, which shows that the system
is nearly edge-on (sin i = 0.9985 +/- 0.0005). Furthermore, we were able to
detect the orbital motion of J2222-0137 in our VLBI observations and measure
the longitude of ascending node. The VLBI astrometry yields the most accurate
distance obtained for a radio pulsar to date, and is furthermore the most
accurate parallax for any radio source obtained at "low" radio frequencies
(below ~5 GHz, where the ionosphere dominates the error budget). Using the
astrometric results, we show the companion to J2222-0137 will be easily
detectable in deep optical observations if it is a white dwarf. Finally, we
discuss the implications of this measurement for future ultra-high-precision
astrometry, in particular in support of pulsar timing arrays.Comment: 22 pages, 7 figures, accepted for publication in Ap
Discovery of Five New Pulsars in Archival Data
Reprocessing of the Parkes Multibeam Pulsar Survey has resulted in the
discovery of five previously unknown pulsars and several as-yet-unconfirmed
candidates. PSR J0922-52 has a period of 9.68 ms and a DM of 122.4 pc cm^-3.
PSR J1147-66 has a period of 3.72 ms and a DM of 133.8 pc cm^-3. PSR J1227-6208
has a period of 34.53 ms, a DM of 362.6 pc cm^-3, is in a 6.7 day binary orbit,
and was independently detected in an ongoing high-resolution Parkes survey by
Thornton et al. and also in independent processing by Einstein@Home volunteers.
PSR J1546-59 has a period of 7.80 ms and a DM of 168.3 pc cm^-3. PSR J1725-3853
is an isolated 4.79-ms pulsar with a DM of 158.2 pc cm^-3. These pulsars were
likely missed in earlier processing efforts due to their high DMs and short
periods and the large number of candidates that needed to be looked through.
These discoveries suggest that further pulsars are awaiting discovery in the
multibeam survey data.Comment: 12 pages, 2 figures, 2 tables, accepted to Ap
Recommended from our members
Identifying and Prioritizing Chemicals with Uncertain Burden of Exposure: Opportunities for Biomonitoring and Health-Related Research.
BackgroundThe National Institutes of Health's Environmental influences on Child Health Outcomes (ECHO) initiative aims to understand the impact of environmental factors on childhood disease. Over 40,000 chemicals are approved for commercial use. The challenge is to prioritize chemicals for biomonitoring that may present health risk concerns.ObjectivesOur aim was to prioritize chemicals that may elicit child health effects of interest to ECHO but that have not been biomonitored nationwide and to identify gaps needing additional research.MethodsWe searched databases and the literature for chemicals in environmental media and in consumer products that were potentially toxic. We selected chemicals that were not measured in the National Health and Nutrition Examination Survey. From over 700 chemicals, we chose 155 chemicals and created eight chemical panels. For each chemical, we compiled biomonitoring and toxicity data, U.S. Environmental Protection Agency exposure predictions, and annual production usage. We also applied predictive modeling to estimate toxicity. Using these data, we recommended chemicals either for biomonitoring, to be deferred pending additional data, or as low priority for biomonitoring.ResultsFor the 155 chemicals, 97 were measured in food or water, 67 in air or house dust, and 52 in biospecimens. We found inĀ vivo endocrine, developmental, reproductive, and neurotoxic effects for 61, 74, 47, and 32 chemicals, respectively. Eighty-six had data from high-throughput in vitro assays. Positive results for endocrine, developmental, neurotoxicity, and obesity were observed for 32, 11, 35, and 60 chemicals, respectively. Predictive modeling results suggested 90% are toxicants. Biomarkers were reported for 76 chemicals. Thirty-six were recommended for biomonitoring, 108 deferred pending additional research, and 11 as low priority for biomonitoring.DiscussionThe 108 deferred chemicals included those lacking biomonitoring methods or toxicity data, representing an opportunity for future research. Our evaluation was, in general, limited by the large number of unmeasured or untested chemicals. https://doi.org/10.1289/EHP5133
Frequency distribution of post race urine pH from Standardbreds compared with Thoroughbreds: research and regulatory significance
The concentration of drugs and drug metabolites in urine samples of racing horses is strongly influenced by urine pH(Tobin, 1981), depending on whether the drugs are weak acids or weak bases. Drugs that are weak acids tend to concentrate in besic urine. In contrast, drugs that are weak bases tend to concentrate in acidic urine. These relationships have a well-established theoretical basis (the Henderson-Hasselbalch relationship) and have been demonstrated repeatedly in experimental animals and man (Tobin, 1981). More recently, evidence suggests that these relationships also occur with clinically and forensically significant agents in equine urine (Wood, et al. 1990; Gerken et al.1991.
The estimated burden of fungal disease in South Africa
Publication fees were paid via funding from a grant from Fonds.Peer reviewedPublisher PD
The estimated burden of fungal disease in South Africa
Background. With a population of 56.5 million, over 7 million persons living with HIV, one of the worldās highest rates of tuberculosis (TB) and a large proportion of the population living in poverty, South Africa (SA)ās fungal disease burden is probably substantial and broad in scope.Objectives. To estimate the burden of fungal disease in SA.Methods. Using total and at-risk populations and national, regional and occasionally global data, we estimated the incidence and prevalence of the majority of fungal diseases in SA.Results. Estimates for the annual incidence of HIV-related life-threatening fungal disease include cryptococcal meningitis (8 357 cases), Pneumocystis pneumonia (4 452 cases) and endemic mycoses (emergomycosis, histoplasmosis and blastomycosis, with 100, 60 and 10 cases per year, respectively). We estimate 3 885 cases of invasive aspergillosis annually. The annual burden of candidaemia and Candida peritonitis is estimated at 5 421 and 1 901 cases, respectively. The epidemic of pulmonary TB has probably driven up the prevalence of chronic pulmonary aspergillosis to 99 351 (175.8/100 000), perhaps the highest in the world. Fungal asthma probably affects >100 000 adults. Mucosal candidiasis is common, with an annual prevalence estimated at 828 666 and 135 289 oral and oesophageal cases, respectively, complicating HIV infection alone (estimates in other conditions not made), and over a million women are estimated to be affected by recurrent vulvovaginal candidiasis each year. Tinea capitis in children is common and conservatively estimated at >1Ā 000 000 cases. The inoculation mycoses sporotrichosis, chromoblastomycosis and eumycetoma occur occasionally (with 40, 40 and 10 cases estimated, respectively). Overall, we estimate that over 3.2 million South Africans are afflicted by a fungal disease each year (7.1% of the population).Conclusions. Significant numbers of South Africans are estimated to be affected each year by fungal infections, driven primarily by the syndemics of HIV, TB and poverty. These estimates emphasise the need for better epidemiological data, and for improving the diagnosis and management of these diseases
Discovery and Follow-up of Rotating Radio Transients with the Green Bank and LOFAR Telescopes
We have discovered 21 Rotating Radio Transients (RRATs) in data from the
Green Bank Telescope (GBT) 350-MHz Drift-scan and the Green Bank North
Celestial Cap pulsar surveys using a new candidate sifting algorithm. RRATs are
pulsars with sporadic emission that are detected through their bright single
pulses rather than Fourier domain searches. We have developed {\tt RRATtrap}, a
single-pulse sifting algorithm that can be integrated into pulsar survey data
analysis pipelines in order to find RRATs and Fast Radio Bursts. We have
conducted follow-up observations of our newly discovered sources at several
radio frequencies using the GBT and Low Frequency Array (LOFAR), yielding
improved positions and measurements of their periods, dispersion measures, and
burst rates, as well as phase-coherent timing solutions for four of them. The
new RRATs have dispersion measures (DMs) ranging from 15 to 97 pc cm,
periods of 240 ms to 3.4 s, and estimated burst rates of 20 to 400 pulses
hr at 350 MHz. We use this new sample of RRATs to perform statistical
comparisons between RRATs and canonical pulsars in order to shed light on the
relationship between the two populations. We find that the DM and spatial
distributions of the RRATs agree with those of the pulsars found in the same
survey. We find evidence that slower pulsars (i.e. ms) are
preferentially more likely to emit bright single pulses than are faster pulsars
( ms), although this conclusion is tentative. Our results are consistent
with the proposed link between RRATs, transient pulsars, and canonical pulsars
as sources in various parts of the pulse activity spectrum.Comment: 18 pages, 13 figures, 5 tables, published in Ap
Young Radio Pulsars in Galactic Globular Clusters
Currently three isolated radio pulsars and one binary radio pulsar with no
evidence of any previous recycling are known in 97 surveyed Galactic globular
clusters. As pointed out by Lyne et al., the presence of these pulsars cannot
be explained by core-collapse supernovae, as is commonly assumed for their
counterparts in the Galactic disk. We apply a Bayesian analysis to the results
from surveys for radio pulsars in globular clusters and find the number of
potentially observable non-recycled radio pulsars present in all clusters to be
< 3600. Accounting for beaming and retention considerations, the implied birth
rate for any formation scenario for all 97 clusters is < 0.25 pulsars per
century assuming a Maxwellian distribution of velocities with a dispersion of
10 km s^{-1}. The implied birth rates for higher velocity dispersions are
substantially higher than inferred for such pulsars in the Galactic disk. This
suggests that the velocity dispersion of young pulsars in globular clusters is
significantly lower than those of disk pulsars. These numbers may be
substantial overestimates due to the fact that the currently known sample of
young pulsars is observed only in metal-rich clusters. We propose that young
pulsars may only be formed in globular clusters with metallicities with
log[Fe/H] > -0.6. In this case, the potentially observable population of such
young pulsars is 447^{+1420}_{-399} (the error bars give the 95% confidence
interval) and their birth rate is 0.012^{+0.037}_{-0.010} pulsars per century.
The mostly likely creation scenario to explain these pulsars is the electron
capture supernova of a OMgNe white dwarf.Comment: 13 Pages, 6 Figures, 4 Tables, to appear in Ap
A millisecond pulsar in a stellar triple system
Gravitationally bound three-body systems have been studied for hundreds of
years and are common in our Galaxy. They show complex orbital interactions,
which can constrain the compositions, masses, and interior structures of the
bodies and test theories of gravity, if sufficiently precise measurements are
available. A triple system containing a radio pulsar could provide such
measurements, but the only previously known such system, B1620-26 (with a
millisecond pulsar, a white dwarf, and a planetary-mass object in an orbit of
several decades), shows only weak interactions. Here we report precision timing
and multi-wavelength observations of PSR J0337+1715, a millisecond pulsar in a
hierarchical triple system with two other stars. Strong gravitational
interactions are apparent and provide the masses of the pulsar (1.4378(13)
Msun, where Msun is the solar mass and the parentheses contain the uncertainty
in the final decimal places) and the two white dwarf companions (0.19751(15)
Msun and 0.4101(3) Msun), as well as the inclinations of the orbits (both
approximately 39.2 degrees). The unexpectedly coplanar and nearly circular
orbits indicate a complex and exotic evolutionary past that differs from those
of known stellar systems. The gravitational field of the outer white dwarf
strongly accelerates the inner binary containing the neutron star, and the
system will thus provide an ideal laboratory in which to test the strong
equivalence principle of general relativity.Comment: 17 pages, 3 figures, 1 table. Published online by Nature on 5 Jan
2014. Extremely minor differences with published version may exis
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